The ability to quantify the level of intermolecular associations between macromolecules in solution is a topic of extreme scientific importance, as such associations typically lead to massive changes in the properties of a polymer solution. For instance, if an associative polymer (AP) associates intramolecularly to form unimolecular polymeric micelles, the AP solution will remain fluid, whereas if the associations take place intermolecularly, the resulting polymeric network will induce a dramatic increase in the solution viscosity. Certainly one of the tools most commonly used to probe intermolecular associations is fluorescence resonance energy transfer or FRET. Since an excited donor (D) can only transfer its energy to a ground-state acceptor (A) if the distance separating D from A (dD-A) is less than twice the Förster radius (Ro), which is itself less than 10 nm for any given D-A pair, evidence of FRET between a D-labeled macromolecule and an A-labeled macromolecule provides strong evidence of intermacromolecular interactions. The strength of these interactions can be inferred qualitatively from the FRET efficiency (EFRET) with EFRET taking values between zero and unity depending on how dD-A averaged over all D-A pairs compares to Ro. Interestingly, a quantitative measure of the actual level of association, such as the molar fraction of macromolecules (finter) involved in intermolecular associations, is rarely provided when FRET is used, probably because of the complex relationship that exists between EFRET and the distribution of dD-A values.